1. Field of the Invention
The present invention relates to an aqueous ink having good hue and high fastness and printing density, use thereof as an ink for inkjet recording, and an inkjet recording method.
2. Description of the Related Art
An inkjet recording method is rapidly spreading and further developing because the material costs are inexpensive, high-speed recording is possible, a noise at the time of recording is low, and color recording is easy.
The inkjet recording method includes a continuous system of continuously flying droplets and an on-demand system of flying droplets according to an image information signal; and its discharge system includes a system of discharging droplets by applying a pressure by a piezo element, a system of discharging droplets by generating bubbles in an ink by heat, a system of using ultrasonic waves, and a system of sucking and discharging droplets by an electrostatic force. Also, aqueous inks, oily inks, and solid (melt type) inks are used as an ink for inkjet recording. Of these inks, aqueous inks are the main current from the standpoints of manufacture, handling properties, odors, safety, and so on.
Colorants which are used in such inks for inkjet recording are required to have such properties that they have good solubility or dispersibility in solvents; they can achieve high-density recording; they have good hue; they are fast to light, heat and active gases in the circumstance (for example, oxidizing gases such as NOx and ozone, and SOx); they have excellent fastness to water and chemicals; they have good fixability to an image-receiving material so that they hardly cause bleeding; they have excellent preservability as an ink; they are non-toxic; they have a high purity; and they are inexpensively available. However, it is extremely difficult to find out colorants, which meet these requirements in high levels.
As azo dyes having good hue, dyes disclosed in JP-A-2003-306623 are known, but any specific combination containing two or more kinds of dyes each having at least one ionic hydrophilic group in the molecule thereof is not disclosed.